RFID antenna modules and increasing coupling

ABSTRACT

A transponder with an antenna module having a chip module and an antenna; a booster antenna having a first antenna structure in the form of a flat coil having a number of turns, an outer end and an inner end, and a second antenna structure in the form of a flat coil having a number of turns, an outer end and an inner end; the inner end of the second antenna structure connected with the outer end of the first antenna structure. The antenna module may be positioned so that its antenna overlaps one of the first antenna structure or the second antenna structure. An antenna module having two additional antenna structures is disclosed. Methods of enhancing coupling are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from and incorporates by reference:

-   -   provisional No. 61/373,269 filed Aug. 12, 2010    -   provisional No. 61/384,219 filed Sep. 17, 2010    -   provisional No. 61/493,448 filed Jun. 4, 2011    -   provisional No. 61/493,611 filed Jun. 6, 2011

TECHNICAL FIELD

The invention relates to “secure documents” such as electronicpassports, electronic ID cards and smart cards having RFID (radiofrequency identification) chips or chip modules and more particularly tomethod and apparatus for increasing RF coupling between the securedocument and external readers, both for powering the RFID chip andtransferring data.

BACKGROUND

A secure document such as an electronic passport, smart card or nationalID card may comprise an inlay substrate or card body having one or morelayers, an RFID chip or chip module, an antenna, and one or moreprotective layers and/or overlay layers bearing user information and/orsecurity markings. The chip module may operate solely in a contactlessmode, such as ISO 14443, or may be a dual interface module which canoperate in contact and contactless mode. The chip module may harvestenergy from an RF signal supplied by an external RFID reader device withwhich it communicates.

The inlay substrate or card body may comprise one or more layers ofPolyvinyl Chloride (PVC), Polycarbonate (PC), polyethylene (PE), PET(doped PE), PET-G (derivative of PE), Teslin™, Paper or Cotton/Noil, andthe like.

The chip module may be a leadframe-type chip module or an epoxy glasstype chip module. Some specific examples of chip modules are disclosedherein.

The antenna conductor may be self-bonding (or self-adhering) wirecomprising; a metallic core (typically, but not necessarily round incross-section) comprising copper, aluminum, doped copper, gold, silver,or Litz wire, and may have a diameter of 0.010-0.50 mm; a first coatingor “base coat” comprising modified polyurethane, and having a thicknessof only a few microns; and a second coating comprising polyvinylbutyralor polyamide, and having a thickness of only a few microns.

A conventional method of mounting an antenna wire to an inlay substrateis to use a sonotrode (ultrasonic) tool which vibrates, feeds the wireout of a capillary, and embeds it into or sticks it onto the surface ofthe inlay substrate, in the form of a flat coil, with ends or endportions of the antenna wire connected, such as by thermo compression(TC) bonding, to terminal areas of the chip module. See U.S. Pat. No.6,698,089 and U.S. Pat. No. 6,233,818, incorporated by reference herein.

In the manufacture of high frequency dual interface cards andcontactless smart cards, an inlay containing an antenna or an inlaycontaining an antenna connected to an RFID chip has been required. Theantenna having several turns (4-5) is routed around the perimeter of thecard body to obtain optimum electrical parameters (resistance,inductance, capacitance and Q-factor). Recent developments in chiptechnology have permitted the reduction in the size of the antenna toaccomplish a read-write distance of several centimeters.

US 2010/0176205 ('205 publication), incorporated by reference herein,discloses chip card with dual communication interface. As disclosedtherein:

-   -   According to another alternative embodiment, the device for        concentrating and/or amplifying electromagnetic waves consists        of an antenna comprising at least one coil, disposed in the card        body below the cavity intended for receiving the microelectronic        module.    -   Advantageously, the coils of the antenna of the module are        located on the periphery of the module, and the electric        contacts of the terminal block are located inside the area        defined by the coils of the antenna. Thus, the electromagnetic        flow captured by the coils of the antenna of the module is        maximum, which favourably influences the range of the        contactless communication with the reader. In this embodiment,        the electric contacts of the terminal block of contacts are        preferably arranged in order to comply with ISO standard 7816-2.    -   Advantageously, the coils of the antenna of the module are        located on the same side of the substrate as the microelectronic        chip, and the electric contacts of the terminal block are        located on the opposite face of the substrate.

A problem with an arrangement such as disclosed in the '205 publicationwhich incorporates the antenna into the chip module is that the overallantenna area is quite small (such as approximately 15 mm×15 mm), incontrast with a more conventional antenna which may be formed byembedding several (such as 4 or 5) turns of wire around a periphery ofthe of the secure document, in which case the overall antenna area maybe approximately 80 mm×50 mm (nearly 20 times larger).

Canadian patent application CA 2,279,176, incorporated by reference inits entirety herein, describes a transmission module for a transponderdevice, transponder device and method for operating said device. Theinvention relates to a transmission module (14) for contactlesstransmission of data between a chip (15) and a reading device (12) witha coil arrangement comprising a coupling element (19 and at least oneantenna coil (20) that are electrically interconnected, wherein saidcoupling element is used to produce inductive coupling with atransponder coil (18) which is electrically connected to the chip, andthe antenna coil is used to enable connection to the reading device. Thecoupling element embodied as a coupling coil (19) and the antenna coil(20) are configured differently with respect to the coil parametersaffecting coil impedance.

The published German application DE 4311493 describes in claim 1 adevice (21, 27) used in the production of an identification unit (20) inthe format of a card with a chip (24, 29) provided in a placement modulefor insertion into a recess (22) of a card body, whereby the placementmodule represents a chip carrier module (28) provided with at least onecoil (25, 30) electrically connected to the chip (24, 29) in forming atransponder unit (26, 31). In claim 2, the device according to claim 1is characterized by the chip carrier module (28) having an access sidewith a contact surface (39) and that the transponder unit (31) isarranged on the opposite side of the access side and is electricallyconnected with the contact surface (39).

U.S. Pat. No. 5,084,699 describes a coil assembly for use in aninductively powered transponder including a primary coil and a secondarycoil wrapped around the same coil forming ferrite rod. The primarycoil's leads are left floating while the secondary coil's leads areconnected to the integrated identification circuit of the transponder.There are approximately three times as many turns to the primary coil asthere are turns to the secondary coil. The primary coil is configured toself resonate at the operating frequency of the identification circuitwhen brought within range of an interrogator's magnetic field, therebycreating a voltage across the primary coil having a high sourceimpedance. The secondary coil is configured to resonate at the sameoperating frequency, but to convert the high source impedance level ofthe primary coil to a low source impedance level, which is more suitablefor powering the identification circuit and which substantially matchesthe impedance level of the secondary coil to the impedance level of theinterrogator field, thereby maximizing the quantity of energy which canbe transferred between the interrogator and the transponder.

U.S. Pat. No. 6,142,381 describes a chip card for contact access andcontactless access to a chip arranged in a chip module, wherein the chipmodule is arranged in a recess (59) of a card body (49) such that outercontact surfaces (51) of the chip module are arranged at the surface(60) of the card body (49) and inner contact surfaces (53) of the chipmodule are connected to conductor ends (55, 56) of a coil (57) arrangedin the card body to form a transponder unit, where the coil has the formof a wire coil (57) and the depth (t) of the recess (59) whichaccommodates the chip module is such that wire ends (55, 56) arranged inthe region of the recess (59) have a contact flattening (63) formed bythe machining process for the formation of the recess (59).

U.S. Pat. No. 6,310,778 describes an IC card module (20) for producingan IC card (118) having at least one coil (46) and at least one chip(23) for the formation of a transponder unit, with the chip and the coilbeing connected together by way of a module carrier (21) which renderspossible not only an electrically conductive connection between the chipand the coil, but also an electrically conductive connection with anexternal contact face (38) of the module carrier and the chip, whereinthe IC card module (20) has a retaining device (41) which is at adistance from the external contact face (38) by an offset R and projectslaterally beyond the external contact face, and also a method forproducing an IC card with use of such an IC card module.

U.S. Pat. No. 6,406,935 describes a hybrid-contact contactless smartcard manufacturing process and specifically a manufacturing process forhybrid-contact contactless smart card in which the antenna is on afibrous material such as paper. This process includes a manufacturingstep to screen print the antenna onto the support, a step to laminatethe card body onto the antenna support by hot press molding, a step tomill a cavity in the card body opposite the side of the support bearingthe screen print for housing a module comprised of a chip and adouble-sided circuit and a step for inserting the module in the card.Cutouts made in the corners of the antenna support prior to thelamination step enable the card bodies to be bonded together. The cardthus obtained allows a posteriori viewing of any mechanical misuse towhich it may have been subjected (extreme bending).

U.S. Pat. No. 6,719,206 describes a data transaction card having aninterface for bi-directional contactless communication, and comprising asupport (20) having a cavity (12) for accommodating therein a chipcarrier therein module (10). The chip carrier module comprises asubstrate (11) having a first side (45) and a second side (46), and anintegrated circuit (30) mounted on the first side of the substrate formanaging functions of the data transaction card. A coil antenna (40) iselectrically connected to the integrated circuit for inductive couplingwith remote antenna, connections to the coil antenna being accessiblefrom the first side of the substrate. The chip carrier module ispackaged into one discrete unit so as to be amenable to mechanicalassembly of the data transaction card without requiring additionalelectrical connections between the support and the chip carrier moduleduring or subsequent to assembly. Such a construction allows forefficient mass-production of the data transaction card.

US 2009/0057414 describes a method of manufacturing a microelectronicdevice with contactless operation, mainly for electronic passports. Anantenna is made on a thin, flexible substrate. A perforated sheet thatis thin and calibrated, and that has at least one cavity in itsthickness, is placed on the substrate. A microelectronic chip is placedin each cavity of the perforated sheet and the output contacts of themicroelectronic chip are connected to corresponding terminals of theantenna. The microelectronic chip is protected by sealing off the cavitythat contains the chip. The method is particularly adapted formanufacturing electronic radio frequency identification devices, inparticular for electronic passports.

US 2010/0176205, mentioned above, describes a chip card with a dualcontact and contactless communication interface, including amicroelectronic module (11) and a card body (22) provided with a cavity(23) which can receive the microelectronic module, said microelectronicmodule (11) being formed by a substrate (15), the first face thereofbearing a terminal block of electric contacts (4) and a second facethereof bearing a first microelectronic chip (9) electrically connectedto the terminal block of electric contacts (4) and a second chip (10)electrically connected to the terminals of an antenna (13), the coils ofwhich are disposed on the second face of the substrate of the electronicmodule. The invention is characterised in that the card body (22)includes a device (18) for concentrating and/or amplifyingelectromagnetic waves, which can channel the electromagnetic flowreceived, in particular, from a contactless chip card reader toward thecoils of the antenna (13) of the microelectronic module (11).

US 2010/0283690 describes a secured document in the form of a booklet ofat least one sheet which may be folded about a folding axis, thedocument having a transponder with an electronic chip provided with amemory for storing data and a transponder antenna. The document alsoincludes a foldable amplifier antenna, distinct from the transponderantenna and arranged on the document such that, when the same is open,the amplifier antenna amplifies the electromagnetic flux received by thetransponder antenna to permit communication of the document with aremote reader and, in the closed position of the document, the amplifierantenna reduces the electromagnetic flux received by the transponderantenna beneath a minimum threshold permitting communication of theelectronic chip with a remote reader.

US 2011/0163167 describes a contactless smart card that comprises a cardbody and an electronic module provided with an electronic chip connectedto the terminals of an antenna, the electronic module being arranged ina recess formed in the card body, wherein the exposed surface of theelectronic module comprises at least one graphic security elementcapable of protecting said electronic module and the contactless cardagainst attempts at fraud.

SUMMARY

According to an embodiment of the invention, a transponder may comprise:an antenna module comprising a chip module and at least one antenna; abooster antenna comprising a first antenna structure in the form of aflat coil having a number of turns, an outer end and an inner end, and asecond antenna structure in the form of a flat coil having a number ofturns, an outer end and an inner end; the inner end of the secondantenna structure is connected with the outer end of the first antennastructure; and the outer end of the second antenna structure and theinner end of the first antenna structure are left unconnected. Theantenna module may be is positioned so that its antenna overlaps one ofthe first antenna structure or the second antenna structure. The boosterantenna may have a pattern including at least one rectangular corner;the antenna of the antenna module may have a generally rectangularpattern; the antenna module may be positioned so that at least twoadjacent side edges of the antenna of the antenna module overlie or areclose to one of the first antenna structure or the second antennastructure. An additional antenna module may be provided, having anantenna closely adjacent or overlapping the booster antenna.

The first and second antenna structures may be coupled in closeproximity and voltages induced in the first and second antennastructures have opposite phase from one another, may be formed in thesame layer as one another, with the second antenna structure disposedwithin the first antenna structure, may be formed in layers overlyingeach other, substantially aligned with one another, may be formed asflat coils of embedded wire, or other than embedded wire, having anumber of turns and an overall length of approximately 1200 mm.

According to an embodiment of the invention, an antenna module for atransponder may comprise: a chip module; a first antenna structure whichis an antenna having two ends connected with the chip module; a secondantenna structure which is a stub having an outer end and an inner end,connected with the first antenna structure; and a third antennastructure which is a stub having an outer end and an inner end,connected with the first antenna structure. The inner end of one of thetwo stubs may be connected with one end of the antenna, and the outerend of the other of the two stubs is connected with the other end of theantenna. The antenna module may be incorporated in a secure document.Electronic Passport Cover, Smart Card/ID Card).

The first, second and third antenna structures may be formed in flatcoil patterns having a number of turns, substantially identical with oneanother, may be disposed substantially directly over one another, andmay be formed by embedding wire or by a process other than by embeddingwire.

According to an embodiment of the invention, a method of coupling atransponder comprising an RFID chip module and an antenna to an externalreader may comprise: providing an antenna module comprising a chipmodule and at least one antenna; providing a booster antenna comprisinga first antenna structure in the form of a flat coil having a number ofturns, an outer end and an inner end, and a second antenna structure inthe form of a flat coil having a number of turns, an outer end and aninner end; connecting the inner end of the second antenna structure withthe outer end of the first antenna structure; and leaving the outer endof the second antenna structure and the inner end of the first antennastructure unconnected. The antenna module may be positioned so that itsantenna overlaps one of the first antenna structure or the secondantenna structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made in detail to embodiments of the disclosure,non-limiting examples of which may be illustrated in the accompanyingdrawing figures (FIGS). The figures are generally diagrams. Someelements in the figures may be exaggerated, others may be omitted, forillustrative clarity. Although the invention is generally described inthe context of various exemplary embodiments, it should be understoodthat it is not intended to limit the invention to these particularembodiments, and individual features of various embodiments may becombined with one another.

FIG. 1 is a cross-sectional view diagram of an antenna module, such asmay be used in the invention.

FIG. 1A is a perspective view of a security document which mayincorporate the invention.

FIG. 1B is a perspective view of a security document which mayincorporate the invention.

FIG. 2A is a schematic representation of an antenna module (AM),according to an embodiment of the invention.

FIG. 2B is a cross-sectional view diagram of the antenna module of FIG.2A.

FIG. 2C is a plan view diagram of a secure document, according to anembodiment of the invention.

FIG. 2D is a plan view diagram of a secure document, according to anembodiment of the invention.

FIG. 2E is a plan view diagram of a secure document, according to anembodiment of the invention.

DETAILED DESCRIPTION

Various embodiments will be described to illustrate teachings of theinvention(s), and should be construed as illustrative rather thanlimiting. In the main hereinafter, transponders in the form of securedocuments which may be smart cards or national ID cards may be discussedas exemplary of various features and embodiments of the invention(s)disclosed herein. Many features and embodiments may be applicable toother forms of secure documents, such as electronic passports.

Generally, for purposes of this discussion, a transponder comprises aninlay substrate which may be formed with many layers, at least oneRFID-capable chip or chip module having two terminals for connectingwith an antenna to operate in a contactless mode, including dualinterface (contactless, contact) chip modules.

In the main hereinafter, antenna structures formed by embedding wire inan inlay substrate or card body are discussed as exemplary. However, itshould be understood that the antenna may be formed using a processesother than by embedding wire in a substrate, such as additive orsubtractive processes such as printed antenna structures, coil windingtechniques (such as disclosed in U.S. Pat. No. 6,295,720), antennastructures formed on a separate antenna substrate and transferred to theinlay substrate (or layer thereof), antenna structures etched (includinglaser etching) from a conductive layer on the substrate, conductivematerial deposited in channels of a substrate layer, or the like.

FIG. 1 shows an antenna module (AM) 100 based on an epoxy filmcomprising a substrate 102, having a top and bottom surface, as viewed.The module may measure approximately 15 mm×15 mm. The substrate 102 mayhave a number (such as two) of terminals 104 disposed on its bottomsurface for connecting with an RFID chip 108, which may be adual-interface chip having contactless and contact functionality. Anantenna 110 having a number (such as 12) of turns of conductor (such astraces, or wire) may be disposed on the bottom surface of the substrate102, and connected via the terminals 104 to the RFID chip 108. The topsurface (which may be referred to as the “back side of the epoxymodule”) is provided with a number (such as six) of contacts 112 forinterfacing with an external smart card contact reader (not shown). Asmart card may be manufactured, incorporating the antenna module (AM)100.

FIG. 1A is a perspective view of an example of a security document whichmay be an electronic passport, and shows a security document which maybe an electronic passport having an inlay comprising a RFID chip moduleand an antenna in an inlay substrate such as of Teslin™, and furthercomprising a cover layer such as of “Holliston fabric” disposed over theinlay. The antenna and chip module are well known, and omitted forillustrative clarity.

FIG. 1B is a perspective view of an example of a security document whichmay be a smart card or electronic identification (eID) card having aninlay substrate or card body comprising an RFID or dual-interface chipmodule and an antenna in a multi-layer substrate, and further comprisinga top overlay layer and a bottom layer both of which protect the cardbody and may be provided with printed information or security markings.The antenna and chip module are well known, and omitted for illustrativeclarity.

FIGS. 2A, 2B illustrate an embodiment of an antenna module (AM) 200 fora transponder comprising

-   -   a chip module (CM) 208 having two terminals 208 a, 208 b    -   an inductive wire antenna (A) 210 formed as a flat coil of        embedded wire having a number (such as 12) of turns, and two        ends—an outer end 1 (at the end of an outer one of the turns)        and an inner end 2 (at an end of an inner one of the turns)        -   The overall length of the antenna A may be 400 mm        -   The ends 1 and 2 of the antenna A may be connected to the            terminals of the chip module.        -   The chip module may be disposed within (interior to) the            turns of the antenna A.        -   The outer turn of the antenna A may cross over inner turns            of the antenna A to be routed to the chip module CM.        -   The antenna A is an “antenna structure”.    -   capacitive antenna extensions (or stubs) B and C also formed as        flat coils of embedded wire having a number of turns, and        connected to the inductive wire antenna as described below.        -   The stubs B,C are “antenna structures”

The chip module 208 and antenna A 210 may be disposed in or on a layer222 of a multi-layer antenna substrate 200. The chip module 208 may bedisposed in a recess (pocket) 206 extending partially through the layer222 (as illustrated), or may be disposed in a recess (opening) extendingcompletely through the layer 222, with the chip module 208 beingsupported by an underlying layer 224.

The chip module is illustrated in FIG. 2B “face up”, with its terminalsfor connecting with the antenna A on its top side. Alternatively, thechip module may be orientated “face down” with its antenna-receivingterminals on its bottom side (and extend through the substrate 222, forexample), and another set of terminals (not shown) for a contactinterface on its top side.

Other variations for the AM 200 may include, but are not limited to . ..

-   -   the antenna A may be on the bottom of the layer 222    -   the stub B 212 may be on the bottom of the layer 224    -   the stub C 214 may be on the bottom of the layer 226    -   the stubs B and C may be on the top and bottom surfaces of a        single layer which is either above or below the layer 222

The stub B 212 may be formed as a flat coil of wire having a number(such as 12) of turns and two ends—an outer end 3 of an outer turn andan inner end 4 of an inner turn—in a layer 224 overlying the layer 222.The stub B may have an overall length of approximately 400 mm, and maybe aligned with (directly over) the antenna A.

The stub C 214 may be formed as a flat coil of wire having a number(such as 12) of turns and two ends—an outer end 5 of an outer turn andan inner end 6 of an inner turn—in a layer 226 underlying the layer 222.The stub C may have an overall length of approximately 400 mm, and maybe aligned with (directly under) the antenna A. The stub C may bealigned with (directly under) the stub B. The stubs B and C may beformed by etching, printing, or other processes, instead of (other than)using embedded wire.

In the schematic view of FIG. 2A, the antenna A and stubs B, C are shownlaterally offset from each other. In FIG. 2B, the inductive wire antennaA and capacitive antenna extensions B and C are shown positioned andaligned atop one another. As best viewed in FIG. 2A, the antennastructures A, B, C may each be formed in a flat coil pattern having anumber of turns, an overall length (from end to end), and a footprint(length×width), and may be substantially identical with one another inthese regards. As best viewed in FIG. 2B, the antenna structures A, B, Cmay be disposed substantially directly over one another.

FIG. 2B illustrates that the number of turns, length, width, pitch andpattern of the stubs B, C may be substantially the same (match) as eachother and they may be aligned one atop the other in layers of theantenna module 200 so that their turns are aligned with one another,turn-for-turn. The stubs B, C may also substantially match and bealigned with the antenna A. Capacitance and the resonant circuit isformed between A+B and A+C. Antenna A is shown disposed in a layerbetween the layers for stubs B and C. Antenna A could alternatively bedisposed in a layer above or below both of the layers for stubs B and C.

Dashed lines (- - -) indicate that the inner end 4 of the stub B 212 maybe connected to the outer end 1 of the antenna A 210, such as at theterminal 208 b, and the outer end 5 of the stub C may be is connected tothe inner end 2 of the antenna A, such as at the terminal 208 b. Theouter end 3 of the stub B and the inner end 6 of the stub C may be leftunconnected (remain open).

Alternatively, the vertical arrows (↓, ↑) indicate that the outer end 3of the stub B may be connected to the outer end 1 of the antenna A (suchas at terminal 208 b), and the inner end of stub C may be connected withthe inner end of the antenna A.

Note that in either case, “opposite” (inner versus outer) ends of thestubs B, C are connected to the two ends 1, 2 of the antenna A—in otherwords, the inner end 4 of B and the outer end 5 of C. As used herein,“connected in an opposite sense” means that the inner end of one of thetwo stubs (B or C) is connected with one end of the antenna (A), and theouter end of the other of the two stubs (C or B) is connected with theother end of the antenna (A). It is generally not desirable that the“same” (such as both inner) ends of the stubs are connected with theends of the antenna A. The connections (interconnects) discussed hereincan be made in any conventional manner, such as by vias through layers,traces on layers, bonding, soldering, crimping, welding, etc.

Locating the stubs B and C over each other in close proximity with theantenna A between them forms additional resonant circuits between the Aand the stubs B, C realized by the stray capacitance between the antennastructures A, B, C. The interaction between the coupled stubs B and Cexposed to the same electromagnetic field from the antenna A mayadvantageously reduce the self-resonance (or self-resonant) frequency ofthe antenna A. Stub B is close to antenna A and stub C is close toantenna A, ergo stub B is close to stub C.

In electronics, capacitors and inductors have parasitic inductance andcapacitance, respectively. For a capacitor, the inductance is primarilydue to the physical dimensions including the leads. Since a capacitorand inductor in series creates an oscillating circuit, all capacitorsand inductors will oscillate when stimulated with a step impulse. Thefrequency of this oscillation is the self-resonant frequency (SRF).

The dimensions of the antenna module 200 may be approximately 15 mm×15mm. Due to the relatively small available area, an inductive wire loopof the size of the antenna module may have a self-resonance frequency ofapproximately 75 MHz. The over-layered close coupled antenna structures(stubs B and C) may function as a wire formed capacitor—with open wireends (3 and 6)—that may reduce the resonance frequency of the formedtransponder to a more desirable value of approximately 13˜17 MHz,thereby increasing the voltage and transferred power to the chip module.

In combination with a commercially-available chip module (such as NXPSmartMx or Infineon SLE66, or other) which may be specified with aninput capacitance of approximately 10˜30 pF the assembled transpondercan be matched to a resonance frequency of 13˜17 MHz. See, for example,the following, incorporated by reference herein:

-   -   Product short data sheet, P5CD016/021/041/051 and P5C×081        family, Secure dual interface and contact PM smart card        controller, Rev 3.2—March 2011, 20 pages    -   Preliminary Short Product Information, SLE 66CLX360PE(M) Family,        8/16-Bit Security Dual Interface Controller For Contact Based        and Contactless Applications, Infineon, November 2006, 14 pages    -   SLE 66 CX126PE, short Product Overview, May 2010, 4 pages    -   SmartMX for programmable high-security, multi-application smart        cards, NXP, 2009, 2 pages,    -   mifare DESFire Data Sheet Addendum, Preliminary specification,        Revision 2.0, April 2003, 7 pages M086820_MF3ICD40_ModuleSpec

This principle of over-layered close-coupled wire (or other conductivetrace) antenna structures (stubs B and C) facilitates reducing the spaceconsumption of the antenna A to a minimum, by moving the additional wireturns of structures (stubs) B, C to separate planes. This principle maybe more efficient than connecting a number of inductive wire antennas(with all wire ends connected) in series or in parallel. Capacitiveextensions for the antenna A could be formed by creating moreconventional conductive surfaces (plates) to offset the resonantfrequency. An advantage of using wire is ease of creation using wireembedding technology, and better utilization of space. The antennamodule may have very limited space restrictions.)

Various alternatives to the “solution” discussed above may include, butare not limited to

-   -   having the two stubs B and C in the same layer as one another,        but with their turns interleaved with one another,    -   having one or both of the stubs B and C in the same layer as the        antenna A,    -   having the two stubs B and C in the same layer as one another,        but both on the same side of (i.e., overlying or underlying) the        antenna A.    -   connecting the outer end 3 instead of the inner end 4 of the        stub B to the outer end 1 of the antenna A, and connecting the        inner end 6 instead of the outer end 5 of the stub C to the        inner end 2 of the antenna A,    -   having only one stub (B or C) connected by either its outer or        inner end (one only) to the outer or inner end (one only) of the        antenna A, and it may generally be preferred to connect the ends        opposite-wise (outer end of one to inner end of the other),        although connecting likewise (inner end to inner end, or outer        end to outer end) is also possible.

FIG. 2C illustrates a secure document 240 (which may be referred to as a“transponder”) such as a national ID card incorporating a boosterantenna concept for matching with antenna module 200 (from FIG. 2). Thecard body 242 may measure approximately 80 mm×50 mm. The antenna module200 may measure approximately 15 mm×15 mm.

A booster antenna 250 is shown, and may comprise

-   -   an outer antenna structure (D) 252 formed as a flat coil of wire        having a number (such as 5) of turns and two ends—an outer end 7        of an outer turn and an inner end 8 of an inner turn, and may        have an overall length of approximately 1200 mm,    -   an inner antenna structure (E) 254 formed as a flat coil of wire        having a number (such as 5) of turns and two ends—an outer end 9        of an outer turn and an inner end 10 of an inner turn, and may        have an overall length of approximately 1200 mm,        -   the inner antenna structure (E) may be disposed within but            closely adjacent to the outer antenna structure (D). The            outer antenna structure (D) may surround the inner antenna            structure (E).    -   the outer end 7 of the outer structure 252 may be connected with        the inner end 10 of the inner structure 254 by a “jumper” 253.    -   the inner end 8 of the outer structure and the outer end 9 of        the inner structure are left unconnected, reducing electrical        losses.    -   the “first” and “second” antenna structures 252 and 254 may be        formed in the same layer as one another (as shown),    -   the “first” and “second” antenna structures 252 and 254 may be        formed in layers overlying each other (in a manner similar to        the stubs B and C), substantially aligned with one another,    -   the “first” and “second” antenna structures 252 and 254 may be        connected with the inner end 10 of first structure 252 connected        to outer end 7 of second structure 254, and the outer end 9 of        the inner structure 254 and inner end 8 of the outer structure        252 remaining unconnected (floating).    -   the “first” and “second” antenna structures 252 and 254 may both        be formed in a flat coil pattern having a number of turns, and        substantially identical with one another (somewhat more        identical when overlying each other rather than disposed one        inside the other).

By connecting the inner and outer structures in this manner (inner end10 of inner structure to outer end 7 of outer structure), the inner andouter windings 254 and 252 are coupled in close proximity and the effectis additive since the induced voltage of the inner winding (253) hasopposite phase (phase inversion) than the voltage induced in the outerwinding (252). These connections should not be reversed (7 and 10remaining unconnected and 8 and 9 connected).

By way of example, the self-resonant frequency of the booster antennastructure 250 is created by the stray capacitance forming between thewindings of either 254 or 252 (also taken alone without interfering eachother). Having only one winding structure, either 254 or 252, wouldresult in a higher than desired self-resonant frequency, such asapproximately 40˜50 MHz. The self-resonant frequency may be reduced by(1) increasing numbers of turns (inductance) or (2) increasing ofcapacity (reducing wire pitch). Increasing numbers of turns increasesinductance and lowers self-resonant frequency. In the case wire ends 8and 9 are connected and 7 and 10 remain open, a standard coil would beformed with the number of both wire structures added. This would resultin a certain self-resonant frequency (e.g. 20˜30 MHz). Connecting thewires 252 and 254 as shown (7 connected with 10) reduces theself-resonant frequency to approximately 13˜17 MHz with the same numberof turns or length of wire.

The structures 252 and 254 may be identical with one another, disposedin an aligned manner in two layers of the card, in manner comparable tothat of FIG. 2B with respect to the stubs B and C. In such as case, theymay be referred to as “top” and “bottom” structures, rather than “inner”and “outer”. In either case, the wire length of the two “legs” 252 and254 of the booster antenna 250 should have substantially the same numberof turns and same wire length.

The booster antenna 250 comprises two close-coupled antenna structures,the outer structure 252 and the inner structure 254, each of which maybe formed using techniques other than wire embedding, as discussed withrespect to the antenna structures A,B,C.

The booster antenna 250 may increase the effective operative distancebetween the antenna module 200 and an external reader (not shown) withcapacitive and inductive coupling. It transfers the energy to theantenna module by concentrating the magnetic field generated by a readerantenna at the position where a module is located.

The unconnected ends 8 and 9 of the booster antenna may be locatednearby each other in the middle between the two structures 252 and 254.Through the connection of the two windings by the wire jumper (orstrap), the booster antenna forms a resonance circuit for the operatingfrequency (approx. 13˜17 MHz).

The Wire Jumper (connection between A and B) forces the electricalpotential of point A and B to the same level. Since both structures 252and 254 are exposed to the same magnetic flux of the reader, thevoltages of both wire loops are added. The arrangement of the twowinding sections is important and that the connection causes a phaseinversion and has an additive effect.

The optimized self-resonance frequency of the booster antenna may beapproximately 13˜17 MHz, which may create the closest coupling betweenthe booster antenna and the antenna module, resulting in enhanced(increased) read/write distance with respect to an external reader.

For chip modules having a high input capacitance, such as 70 pf, theantenna module in combination with the booster antenna can be preparedwith a single inductive antenna (etched or wire coil). For example, achip module having only antenna A (without stubs B and C).

The antenna module (AM) 200 may be positioned so that its antenna Aoverlaps (overlies) only the inner structure 254, such as 2 of the 3windings (turns) of the inner structure (as shown), or alternatively sothat its antenna a overlaps only the outer structure 252. The AM mayalso be located inside of (within) the inner structure 254, close to theinner winding thereof, without overlapping. The AM may also bepositioned to that its antenna A overlaps both of the inner and outerstructures, but this is not recommended.

The AM may also be located at a corner of the rectangular pattern of thebooster antenna 250 so that two adjacent side edges of the AM (namely,its antenna A) overlie or are close to the inner structure 254. This isindicated by AM 200A (dashed lines) located close to the top left cornerof the booster antenna. Additionally, it is possible to use two AMs(each having its own chip module and antenna), for multi-applicationtransponders and additional security. This is indicated by AM 200B(dashed lines) located close to the bottom left corner of the boosterantenna, with its antenna would be closely adjacent or overlapping thebooster antenna, in the manner of AM 200 or AM 200A.

It should be understood that any of the antenna module (AMs) describedherein interacting with the any of the booster antennas described hereinmay be a commercially-available product having only the antenna A,without the stubs B and C. (They can also be with antenna modules withstubs, as in FIG. 2A, 2B.)

FIG. 2D illustrates a modified booster antenna geometry for a securedocument 240D. The booster antenna 250D is shown without any detail,simplified, for illustrative clarity, but may have inner and outerstructures connected in opposite phase, as described with respect to thebooster antenna 250, and may be formed on a card body 242D. The upperright corner (as viewed) of the booster antenna is formed with a“cutout” or “jog”, forming two right angles. An AM 200D is disposed at acorner of the booster antenna so that two sides of the AM are adjacentor overlapping (as shown) the booster antenna.

FIG. 2E illustrates a modified booster antenna geometry for a securedocument 240E. The booster antenna 250E is shown without any detail,simplified, for illustrative clarity, but may have inner and outerstructures connected in opposite phase, as described with respect to thebooster antenna 250, and may be formed on a card body 242E. The boosterantenna is provided with a “cutout” or “jog”, forming four right anglesalong a side thereof. An AM 200E is disposed in the jog so that threeadjacent sides of the AM are adjacent (as shown) or overlapping thebooster antenna. Alternatively, the AM could be adjacent on only one ortwo sides, and overlapping on the remaining two or one sides. Note thatin this configuration, the AM is outside of the booster antenna, andcoupled with the outer structure thereof.

The various patterns for antenna structures (A,B,C,D,E, 250, 250D, 250E)are all “generally rectangular”. In the patterns of FIGS. 2D, 2E—havingcutouts or jogs—, there are more than four rectangular corners. Itshould be understood that other patterns may be suitable, such as ovalto avoid sharp corners, or zigzag (meandering) to increase the overalllength of the antenna structure and the like.

Witnessing the Antenna Wire

In the production of inlays for secure documents such as nationalidentity cards, residence permit cards and drivers licenses, the centralstack-up of the inlay with an array of transponder sites can be made upof two layers of Teslin™ adhesively attached, with the transponders orbooster antennae sandwiched between the two layers. At the secureprinters or personalization bureau, the Teslin™ inlay can bepersonalized with the credentials of an individual card holder at eachsite in the array using a laser printer.

In forming an antenna on Teslin™ using wire embedding, it is known thatthe antenna wire does not penetrate completely into the material duringultrasonic scribing, requiring a lamination process to press theembedded wire antenna entirely into the material. This method ofinstalling an antenna wire into the porous material Teslin™ has a numberof disadvantages. During processing of the inlay in a laser printer, theantenna wire can become dislodged, extending or protruding above thesurface of the inlay, affecting the quality of the printing. Thisshow-through (witnessing) of the antenna is caused by the bending of thematerial from the pressure of the rollers in the printer. In addition,the optical appearance of the antenna or module position in the finishedcard is undesirable.

To eliminate the witnessing of the wire on the top surface of an inlaysubstrate, (monolayer or multi-layered), caused by the mechanicalmovement of the antenna wire or the expansion of the material atcompressed positions, it may be proposed in 61/493,448 filed Jun. 4,2011 or 61/493,611 filed Jun. 6, 2011 that interrupted trenches like arailway track, a continuous pattern of ditches separated by bridges or acontinuous pattern of holes are formed by means of laser ablation in theTeslin™ substrate for receiving the antenna wire, and the antenna wireis installed (laid) into the track removing the need for the pressingoperation associated with ultrasonic embedding of the antenna wire. Theantenna wire is held in place by an interference type fit, at “pinchpoints” between the bridges or holes. A recess to accommodate the chipmodule may also be laser ablated, so that after positioning of the chipmodule, it is flush with the surface of the inlay substrate.

In a two layered inlay, an antenna is installed at each transponder sitein the array and respectively connected to a chip module residing in arecess or pocket, and the covering or second layer is adhesivelyattached to the layer hosting the transponder sites. To reduce thetransparency of the Teslin material at the position of the antenna andmodule, it may be advantageous to abrasively treat the surface of thesecond layer of Teslin™ creating a rough surface, before applyingadhesive for attachment to the transponder layer.

In processing inlay sheets in a printer or a passport booklet machine,it may be advantageous to create a notch in the inlay to indicate theorientation of the transponder(s) or booster antenna(e). The notch maybe in one layer of a two layer construction, for example, in the case ofan e-cover inlay consisting of a monolayer of Teslin™ and a covermaterial, the notch may only be in the Teslin™ layer having a depth ofone millimeter and a width of one centimeter.

While the invention has been described with respect to a limited numberof embodiments, these should not be construed as limitations on thescope of the invention, but rather as examples of some of theembodiments. Those skilled in the art may envision other possiblevariations, modifications, and implementations that are also within thescope of the invention, based on the disclosure(s) set forth herein.

What is claimed is:
 1. A transponder comprising: an antenna module comprising a chip module and at least one antenna; a booster antenna comprising a first antenna structure in the form of a flat coil having a number of turns, an outer end and an inner end, and a second antenna structure in the form of a flat coil having a number of turns, an outer end and an inner end; the inner end of the second antenna structure is connected with the outer end of the first antenna structure; and the outer end of the second antenna structure and the inner end of the first antenna structure are left unconnected.
 2. The transponder of claim 1, wherein: the first and second antenna structures are coupled in close proximity and voltages induced in the first and second antenna structures have opposite phase from one another.
 3. The transponder of claim 1, wherein: the antenna module is positioned so that its antenna overlaps one of the first antenna structure or the second antenna structure.
 4. The transponder of claim 1, further comprising: an additional antenna module having an antenna closely adjacent or overlapping the booster antenna.
 5. The transponder of claim 1, wherein: the first and second antenna structures are formed in the same layer as one another; the second antenna structure is disposed within the first antenna structure.
 6. The transponder of claim 1, wherein: the first and second antenna structures are formed in layers overlying each other, substantially aligned with one another.
 7. The transponder of claim 1, wherein: the first and second antenna structures are each formed as flat coils of embedded wire, or other than embedded wire, having a number of turns and an overall length of approximately 1200 mm.
 8. The transponder of claim 1, wherein: the booster antenna has a pattern including at least one rectangular corner; the antenna of the antenna module has a generally rectangular pattern; and the antenna module is positioned so that at least two adjacent side edges of the antenna of the antenna module overlie or are close to one of the first antenna structure or the second antenna structure.
 9. An antenna module for a transponder comprising: a chip module; a first antenna structure which is an antenna having two ends connected with the chip module; a second antenna structure having an outer end and an inner end, one of which is connected with the first antenna structure, the other of which is left unconnected; and a third antenna structure having an outer end and an inner end, one of which is connected with the first antenna structure, the other of which is left unconnected.
 10. The antenna module of claim 9, wherein: the inner end of one of the two stubs is connected with one end of the antenna, and the outer end of the other of the two stubs is connected with the other end of the antenna.
 11. The antenna module of claim 9, wherein: the first, second and third antenna structures are formed in a flat coil pattern having a number of turns, and are substantially identical with one another.
 12. The antenna module of claim 9, wherein: the first, second and third antenna structures are disposed substantially directly over one another.
 13. The antenna module of claim 9, wherein: the first, second and third antenna structures are formed by embedding wire.
 14. The antenna module of claim 9, wherein: the first, second and third antenna structures are formed other than by embedding wire.
 15. The antenna module of claim 9, further comprising: incorporating the antenna module in a secure document.
 16. A method of coupling a transponder comprising an RFID chip module and an antenna to an external reader comprising: providing an antenna module comprising a chip module and at least one antenna; providing a booster antenna comprising a first antenna structure in the form of a flat coil having a number of turns, an outer end and an inner end, and a second antenna structure in the form of a flat coil having a number of turns, an outer end and an inner end; connecting the inner end of the second antenna structure with the outer end of the first antenna structure; and leaving the outer end of the second antenna structure and the inner end of the first antenna structure unconnected.
 17. The method of claim 16, further comprising: positioning the antenna module so that its antenna overlaps one of the first antenna structure or the second antenna structure. 